At light throttle opening speeds of 35 to 40 mph up to freeway cruise in Overdrive, the carburetor delivered consistent air-fuel ratios of between 13.0:1 and 13.5:1 which was close to ideal. The engine runs a GM Performance Parts hydraulic roller Hot cam (218/228 degrees at 0.050), so even with this mild cam, the engine may not like a leaner ratio, but at least this gives us a starting point from which to do some tuning experiments in search of better mileage.
One area that car crafters may not be aware of is that most carburetors at very light throttle openings are actually running on the idle circuit rather than the main metering circuit, even if the car is equipped with an Overdrive. In this case, we tried leaning out the idle mixture screws slightly to see if that would improve the part-throttle air-fuel ratio. This leaned out the steady-state air-fuel ratio but caused driveability problems, so we will have to try a different technique.
The next best thing will be to data-log all this information during a complete dragstrip run so you can use a computer to plot the data in a spreadsheet format to study more closely what the engine is experiencing during a complete run. Then you can make changes based on the information the LM-1 delivers. What's even better is that you don't have to place the laptop on board the car during the run. You merely hit the "record" button and the LM-1 will capture up to 44 minutes of data-logging information with a sample rate of 12 times per second. We've done this with much more expensive equipment and discovered amazing things about carburetors on the dragstrip.
ConclusionThe beauty of the Innovate Technology LM-1 is that it is not only inexpensive, but completely portable and capable of delivering extremely accurate data that until now could only be obtained using very expensive test equipment. Now anyone can accurately measure air-fuel ratio and get a leg up on tuning any engine for both optimal power and better driveability.